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CONTENTS
Volume 5, Number 2, August 2013
 

Abstract
Linear and nonlinear time history analyses have been becoming more common in seismic analysis and design of structures with advances in computer technology and earthquake engineering. One of the most important issues for such analyses is the selection of appropriate acceleration time histories and matching these histories to a code design acceleration spectrum. In literature, there are three sources of acceleration time histories: artificial records,synthetic records obtained from seismological models and accelerograms recorded in real earthquakes. Because of the increase of the number of strong ground motion database, using and scaling real earthquake records for seismic analysis has been becoming one of the most popular research issues in earthquake engineering. In general, two methods are used for scaling actual earthquake records: scaling in time domain and frequency domain. The objective of this study is twofold: the first is to discuss and summarize basic methodologies and criteria for selecting and scaling ground motion time histories. The second is to analyze scaling results of time domain method according to ASCE 7-05 and Eurocode 8 (1998-1:2004) criteria. Differences between time domain method and frequency domain method are mentioned briefly. The time domain scaling procedure is utilized to scale the available real records obtained from near fault motions and far fault motions to match the proposed elastic design acceleration spectrum given in the Eurocode 8. Why the time domain method is preferred in this study is stated. The best fitted ground motion time histories are selected and these histories are analyzed according to Eurocode 8 (1998-1:2004) and ASCE 7-05 criteria. Also, characteristics of both near fault ground motions and far fault ground motions are presented by the help of figures. Hence, we can compare the effects of near fault ground motions on structures with far fault ground motions\' effects.

Key Words
selection of earthquake records; scaling of earthquake records; time domain scaling; frequency domain scaling

Address
Karadeniz Technical University, Department of Civil Engineering, 61080, Trabzon, Turkey

Abstract
This paper presents the results of an experimental program concerning the efficiency of a specific strengthening technique which utilizes a small steel link element connected to the R/C frame through bracing elements. Brittle types of failure, especially at the connections between steel and concrete elements, can be avoided by appropriate design of the local details. Five single storey one bay R/C frames scaled 1:3 were constructed according to older codes with substandard details. The first one was a typical bare reference frame. The other four were identical to the first one, strengthened by steel bracing elements. The behavior of the strengthened frames is described with respect to the reference bare frame. The concrete frames were constructed according to older code provisions by the use of smooth steel bars, low strength concrete, sparsely spaced stirrups and substandard details. The strengthening scheme aimed to the increase of both strength and deformation capacity of the original R/C frame. The inelastic deformations are purposely concentrated to a short steel link element connecting the steel bracing to the R/C frame. The results show that the steel link element can increase considerably the strength and the energy dissipation capacity of the frame.

Key Words
strengthening techniques; steel braced R/C frames; heal link; energy dissipation capacity

Address
Aristotle University of Thessaloniki, Faculty of Engineering, School of Civil Engineering
Laboratory of R/C and Masonry Structures, Thessaloniki, 54124, Greece

Abstract
We study seismically induced, anti-plane strain wave motion in a non-homogeneous geological region containing tunnels. Two different scenarios are considered: (a) The first models two tunnels in a finite geological region embedded within a laterally inhomogeneous, layered geological profile containing a seismic source. For this case, labelled as the first boundary-value problem (BVP 1), an efficient hybrid technique comprising the finite difference method (FDM) and the boundary element method (BEM) is developed and applied. Since the later method is based on the frequency-dependent fundamental solution of elastodynamics, the hybrid technique is defined in the frequency domain. Then, an inverse fast Fourier transformation (FFT) is used to recover time histories; (b) The second models a finite region with two tunnels, is embedded in a homogeneous half-plane, and is subjected to incident, time-harmonic SH-waves. This case, labelled as the second boundary-value problem (BVP 2), considers complex soil properties such as anisotropy, continuous inhomogeneity and poroelasticity. The computational approach is now the BEM alone, since solution of the surrounding half plane by the FDM is unnecessary. In sum, the hybrid FDM-BEM technique is able to quantify dependence of the signals that develop at the free surface to the following key parameters: seismic source properties and heterogeneous structure of the wave path (the FDM component) and near-surface geological deposits containing discontinuities in the form of tunnels (the BEM component). Finally, the hybrid technique is used for evaluating the seismic wave field that develops within a key geological cross-section of the Metro construction project in Thessaloniki, Greece, which includes the important Roman-era historical monument of Rotunda dating from the 3rd century A.D.

Key Words
SH-waves; anisotropy; inhomogeneity; poroelasticity; tunnels; local site effects; seismic response; hybrid FDM-BEM

Address
Department of Civil Engineering, Aristotle University, 54124 Thessaloniki, Greece
Institute of Engineering Seismology and Earthquake Engineering, P.O. Box 53, 55102 Thessaloniki, Greece
Institute of Mechanics, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
Institute of Mathematics and Informatics, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria

Abstract
Practical seismic assessment and design of retrofit for the multitude of small ecclesiastical monuments that abound in the Balkans is the subject of this work. Application of the proposed procedures and methodologies are illustrated in an example case study, a small byzantine church located in Western Greece, which is the region with the highest seismicity in Europe. The church, known as the Fragavilla Monastery, had remained almost undamaged for 800 years, until 1993 when the Pyrgos earthquake caused critical damage mainly in the vaults. Linear elastic analysis to the recorded ground motion, capped by a biaxial failure criterion reproduced the developed damage. The same modelling and analysis procedure was subsequently used for assessment of the intended retrofitting measures. Proposed retrofitting measures included mitigation of the undesirable implications of past interventions along with a combination of strengthening schemes with externally bonded AFRPs strategically placed in the structure. The effectiveness of the proposed solutions is gauged by successful reduction of stress intensity in the critical regions and mitigation of stress localization throughout the structure.

Key Words
brickwork and masonry; load bearing masonry; historical buildings, structures and design; conservation; restoration

Address
Department of Civil Engineering, University of Patras, Greece

Abstract
Excessive vibrations induced by earthquake excitation and wind load are an obstacle in design and construction of tall and super tall buildings. An innovative vibration control structure system (Mega-Sub Controlled Structure System-MSCSS) was recently proposed to further improve humans comfort and their safeties during natural disasters. Preliminary investigations were performed using a two dimensional equivalent simplified model, composed by 3 mega-stories. In this paper, a more reasonable and realistic scaled model is design to investigate the dynamical characteristics and controlling performances of this structure when subjected to strong earthquake motion. The control parameters of the structure system, such as the modulated sub-structures disposition; the damping coefficient ratio (RC); the stiffness ratio (RD); the mass ratio of the mega-structure and sub-structure (RM) are investigated and their optimal values (matched values) are obtained. The MSCSS is also compared with the so-called Mega-Sub Structure (MSS) regarding their displacement and acceleration responses when subjected to the same load conditions. Through the nonlinear time history analysis, the effectiveness and the feasibility of the proposed mega-sub controlled structure system (MSCSS) is demonstrated in reducing the displacement and acceleration responses and also improving human comfort under earthquake loads.

Key Words
mega-sub controlled structure; vibration control; control effectiveness; structural optimization; modulated sub-structures; viscous damper

Address
School of Civil Engineering, Tongji University, Shanghai 200092, China
School of Mechanic, Civil and Architectural Engineering, Northwestern Polytechnical University, Xian
710129, China

Abstract
Typically, beams that form part of structural systems are subjected to vertical distributed loading along their length. Distributed loading affects moment and shear distribution, and consequently spread of inelasticity, along the beam length. However, the finite element models developed so far for seismic analysis of frame structures either ignore the effect of vertical distributed loading on spread of inelasticity or consider it in an approximate manner. In this paper, a beam-type finite element is developed, which is capable of considering accurately the effect of uniform distributed loading on spreading of inelastic deformations along the beam length. The proposed model consists of two gradual spread inelasticity sub-elements accounting explicitly for inelastic flexural and shear response. Following this approach, the effect of distributed loading on spreading of inelastic flexural and shear deformations is properly taken into account. The finite element is implemented in the seismic analysis of plane frame structures with beam members controlled either by flexure or shear. It is shown that to obtain accurate results the influence of distributed beam loading on spreading of inelastic deformations should be taken into account in the inelastic seismic analysis of frame structures.

Key Words
seismic analysis; finite element; distributed inelasticity; beam members; distributed loading

Address
City University London, School of Engineering and Mathematical Sciences, Department of Civil Engineering,
London EC1V 0HB, United Kingdom


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